In modern motor vehicles, as a rule, at least one sensor is situated in the exhaust system of the combustion engine, the sensor first being operational after a specific temperature is exceeded. For example, the sensor may be a lambda probe. The sensor is heated by the hot exhaust gases blowing past. In operation, it should have a nominal temperature of typically 750° C. In order to reach the minimum temperature of the sensor as quickly as possibly after the start, and also to ensure the minimum temperature in operating ranges in which the heating power of the exhaust gases alone is not sufficient for that purpose, it is customary to provide the sensor with an electrical heating device. In the event of a defect in the heating device, the operativeness of the sensor may be sharply restricted.
German Patent Application No. DE 39 28 709 describes a method and a device for checking the operativeness of a heating device for the exhaust gas analyzer probe and its leads. In that case, after the heating device is switched on, the readiness of the exhaust gas analyzer probe for operation is determined at two successive times. If it is not ready for operation after the first time has elapsed and is operationally ready after the second time has elapsed, a malfunction of the heating device is inferred. This function diagnosis is based on the assumption that the exhaust gas analyzer probe reaches its minimum operating temperature more quickly when the heating device is switched on and operating correctly, than when heated up solely by the exhaust gases. Thus, this method is suitable for checking the readiness of the exhaust gas analyzer probe for operation. Requirements of the California Air Resources Board CARB, which require that the malfunction of parts relevant to the exhaust gas (among which is also the probe heating) be detected and indicated, are thereby satisfied. Meanwhile, in the European market, it is also mandatory to monitor the heating current or an alternative variable.
An object of the present invention is to provide a method which determines the rated heating power and control heating power of an electrical heating of a probe situated in the exhaust system of an internal combustion engine, and monitors the total heating power as the sum of both, such that overheating of the probe is prevented.
It is a further object of the present invention to provide a device for implementing the method.